Rapid cycle digester



Jan. 9, 1962 A. J. HORSTMAN ETAL RAPID CYCLE DIGESTER Filed Sept. '7, 1954 INVENTORti Huron d. Hons-mn/v LE: 5. EBERHARDT United States Patent O 7 3,016,088 RAPID CYCLE DIGES'IER Anton J. Horstman and Lee E. Eberhardt, Springfield,

Ohio, assignors to The Bauer Bros. Company, Springfield, Ohio, a corporation of Ohio Filed Sept. 7, 1954, Ser. No. 454,590 3 Claims. (Cl. 162-242) This invention relates to the production of cellulose pulp from plant materials, and particularly tothe pulping and steaming of wood chips. Thus, while not so limited, the instant invention has especial reference to the cooking or digesting of wood chips, this being a process of reduction utilizing steam or a chemical liquor or both in a pressure vessel to form a pulp material out of raw wood chips for use in a variety of wood products. I

The instant invention has in view an improvement in the production of wood pulp as described by which the size of the pressure vessel or digester may be materially reduced without any corresponding reduction in the quantity of wood chips treated over a working period of, for example, one day. It is contemplated in this connection to introduce a principle of rapid cycle operationina ,digester whereby although the capacity of the digester is relatively small its total work capacity is relatively large due to a substantial shortening of the work cycle. For example, in the steaming of wood for insulation material or hardboard, a cycle may be completed in from six to unlikely to get out of repair.

A further object of the invention is to provide for quick raising and lowering of pressure values in the digester,

permitting the use of very high pressures and temperatures.

A further object of the invention is to obviate the necessity for repeat cycles in the digesting operation, thus fur,- ther reducing the time required for a complete operational cycle and permitting the use of relatively high temperatures and pressures. a

A still further object of the invention is to provide for the pressurizing of the digester by means of air, steam or hydrostatic pressures when the chemical cooking liquor is contained therein. 7 v I A still further object of the invention is to-maintain a substantially constant level of liquor in the digester during impregnation and cooking portions of the operational cycle.

A further object of the invention is to provide a rapid cycle digester for cellulosicmaterial and a'method of operation embodying the advantageous features, the inherent meritoriouscharacteristics and the mode of operation herein set forth or their equivalents.

With the above primary and other incidental objects in view as will more fully appear in the specification,.the invention intended to be protected by Letters fPatent'consists of the features of construction, the parts and combinations thereof, and the mode of operation, as hereinafter described or illustrated in the accompanyingdrawings, or their equivalents. a

In the accompanying drawing, wherein is shownone but obviously not necessarily the only form of embodi- .ment of the invention,

.tom of a reservoir 33 of cooking liquor.

.by way of the opening 11.

Patented Jan. 9, 1962 FIG. 1 is a view in longitudinal section (partly diagrammatic) of a digester used in the practice of the presently disclosed form of the invention; and

FIG. 2 is a diagram. of a digesting system used in the practice of the disclosed form of the invention.

Like parts are indicated by similar characters of reference throughout the several views. I

Referring to the drawings, the apparatus for practice of pulping andsteaming of fibrous material in accordance with the present invention may include as shown in FIG. 1 a pressure vessel or digester 10. The vessel 10 has substantially the shape of a closedcylindrical tank. Axial openings 11 and 12 are at the top and bottom of the tank 10 and other openings 13 and 14 are at the top of the tank, and still other openings 15 and 16 are at the bottom of the tank. The several described openings define bosslike projections to which may be connected respective'pipe lines 17 to 23 respectively. A shut-off valve 24 is interposed between the pipe 17 and opening 11 and is operated by remote control by means including a pneumatic cylinder 25. Similar valve assemblies comprising a valve and a pneumatic cylinder are mounted between the several pipe" lines 18 to 23 and their respective tank openings 12 to 16 and are indicated respectively at 26 to 31.

Within the vessel 10 is a conical strainer 32 arranged with its open base end facing the upper end of the vessel 10 and with its lower apex end facing the lower end of the vessel in registry with the opening 12. Theside walls of the vessel 10 are relatively straight so that within the lower portion of the vessel. there is a relatively large amount of space between the shell of the vessel and the strainer 32.

The pipe '17 communicates with a source of supply of raw wood chips or other fibrous material to be treated. The, pipe 18 provides for discharge of the treated pulp material and extends to a suitable place of discharge. The pipe 19 is open to exhaust, asto the atmosphere. The pipe 21 communicates with a source of pressure which in some instances is air and in other instances steam, and means may be provided for connecting to these sources alternatively. The pipe 22 communicates with a source of steam. p

The pipe 23 communicates, as indicated, with the bot- I A pipe 34 parallels the pipe 23 and also communicates with vessel opening 16 at its one end and with the lower. part of the reservoir 33- at its other end. The pipe 23 has, in addition to the valve assembly 31, a pump 35. The pipe 34 has interposed therein spaced apart shut off valves 36 and 37. a

Opening into the pipe 34 between the valves 36 and 37 is a conduit 38 extending from the bottom of a pressure tank 39. A shut-off valve 41 is in the conduit 38. Extending into the upper end of the tank 39 is a pipe 42 leading from the previously mentioned source of airor steam pressure and having interposed therein a shut-off valve 43. The upper part of the tank 39 also is connected by a pipe 44 with the reservoir 33. A pump 45 is in the pipe 44, as is a shut-off valve 46 located between the pump 45 and tank 39.

In the operation of the apparatus and practice of the invention, the fibrous material, which, forexample, may be wood chips, is introduced into the pressure vessel 10 The valve 24 is, of course, at this time open as is the exhaust valve 27. The remaining valves in the system' areat this time closed, although as the vessel 10 becomes partly filled the valve 29 is opened to admit steam under pressure to the vessel at the bottom thereof. Continued filling of the vessel thus is accompanied by an: expelling of air therefrom, the

steam from opening "15 -rising through the tank'and 3 through the massed chips therein driving contained air toward the upper end of the vessel to and through exhaust opening 13.

When the digester has been filled with chips all of the valves except valve 29 are closed and steam is permitted to fiow into the vessel. Since the vessel is not now vented the internal pressure in the vessel rapidly rises. It may be noted in this connection that the screen 32 offers little or no resistance to passage of the incoming steam and there is therefore no material reduction in the rate of pressure increase as a result of frictional loss. The steam pressure is allowed to build up in the vessel 10 until it reaches a high value in excess of 75 pounds per square inch and is then stabilized at a selected high pres sure value for a predetermined time interval which may range from zero to five minutes. At the end of that time the exhaust valve 27 is opened with the result that the pressure in the vessel is rapidly reduced.

The described steaming of the wood chips restores the wood to a uniform moisture level throughout the mass of chips, allowing the uniform cooking of chips of different moisture levels, for example, combinations of green chipped wood and kiln driedwood or chipped veneer waste.

The raising of pressure within the vessel as indicated and the subsequent lowering of such pressure prior to introduction of cooking liquor makes the chips, although of varied types, highly receptive to the introduction and absorption of cooking liquor.

In reducing the steam pressure as described, the exhaust valve 27 is held open until a predetermined low pressure value is attained, which value may vary from some five to fifty pounds per square inch but which is held at a super atmospheric value so that no air may return to the vessel and replace that which was exhausted as above described. Now, the steamed wood chips may be removed from the vessel or their treatment may be continued through addition of a cooking liquor.

In the former instance, the valve 26 is opened and the entire charge of chips in the vessel is blown out the opening 12 by the contained pressure. In the event liquor is to be added to the pressure vessel 10,'such liquor is drawn into the vessel by way of reservoir 33 and placed under pressure for a predetermined time interval. Thus, the charge of chips is thoroughly impregnated with the liquor. This step may then be followed by further treatment after which the chips are discharged.

Thus, following impregnation, the fibrous material can be cooked in the presence of liquor or the liquor can be evacuated and the material cooked in a so-called vapor phase without liquor. During impregnation considerable volumes of the liquor enter the cell structure of the fibrous material and cause a lowering of the cooking liquor level unless replenished. The pressure tank 39 serves a function in this connection as will appear in the operational examples to follow.

In the simple steaming of wood chips for use in making insulation material or hardboard, the initial steam pressure as above described may be raised to a value of about 300 pounds per square inch and held at this pressure for about five minutes. The steam then is permitted to exhaust until a lower pressure value of about 50 pounds per square inch is achieved and at this time the discharge valve 26 is opened and the contained charge of chips is expelled from the vessel. A complete cycle of operation in this instance may be completed in from six to eight minutes.

In a typical operation involving the use of liquor for cooking, the initial steam pressure as above described is raised to a selected value in the range of 75 to 300 pounds per square inch and is held there for a time interval ranging from zero to four minutes. The pressure is then reduced to a value between and 25 pounds per square inch by opening of valve 27. After such reduction in pressure the valve 31 in line 23 is opened and the pump 35 in such line is actuated to start liquor flowing from the reservoir 3?: into the vessel 10 by way of the bottom thereof. When the vessel is filled or substantially filled with liquor the valve 31 is closed and operation of the pump 35 is discontinued. The pipe 21 is connected to a source of air pressure and valve 28 controlling flow through the pipe 21 and opening 14 is opened permitting application of air pressure upon the cooking liquor, the air pressure being permitted to rise to a selected value in a range of to 300 pounds per square inch where it is held for one to five minutes. The air pressure then is relieved and steam is admitted by way of the valve 28 While at the same time valves 36 and 37 are opened, the result being that the liquor in the vessel It? is returned to the reservoir 33. Once the digester or pressure vessel is'filled, it may be noted, the pressure is never again reduced to atmospheric so that there are no admissions of air. 7 By having the steam admitted to the vessel at the same time the wood chips are added thereto most ofthe air is driven out of the vessel and so excluded from the operating cycle.

According to another operational procedure, instead of connecting the valve 28 alternatively to air and to steam, it is connected only to a source of steam. Also, the valve 28 may be kept closed during the liquor impregnation part of the cycle and the means for replenishing absorbedliquor may reside in the pump 45. Thus, after the vessel 10 has been filled by operation of the pump 35, which preferably is of the low pressure high volume type, the valve 31 is closed and valves 36, 41 and 46 are opened. The pump 45 then is started with the result that a hydrostatic pressure is applied through the tank 39, pipe 38, and pipe 34 to the liquor contained in the vessel 10 insuring the existence of a desired-pressure in the vessel and the maintaining of a full volume of liquor. The pump 45 is preferably of the high pressure low volume kind. A similar hydrostatic pressure may be established by opening valve 43 to ,admit air or steam under pressure to the upper part of the tank 39 where it is applied to the liquor in the tank and thereby to the liquor in the vessel 10.

Upon completion of the impregnation of the chips in accordancewith either of the above methods, the chips are then cooked. If a vapor phase cooking technique is employed, the liquor which has been introduced into the vessel is withdrawn or blown back into the reservoir 33 as previously described. Thereupon valve 36 is closed and valve 29 is opened to admit steam to the vessel. The chips within the vessel are thereby cooked by the steam entering through valve 29 for a period of from 5 to 15 minutes. The length of time is governed by the type of material being processed and by the particular type of finished product desired.

After completion of the cooking cycle, valve 29 is closed, discharge valve 26 is opened, and the upper steam valve 28 is opened. Steam entering the vessel through valve 28 blows the cooked material from the vessel through the discharge opening 18 into a receiver (not shown). Thereupon the cooked chips may be further treated in accordance with the end result desired.

If it is desired to cook the chips in the presence of the liquor, the liquor is not withdrawn from the vessel after the impregnation operation. Instead valve 36 remains closed and valve 28 is opened to admit steam to the vessel which is filled with both chips and cooking liquor. Liquor cooking of the chips takes considerably longer than the vapor cooking thereof since it is necessary to raise the temperature of the cooking liquor as well as the mass of the chips.

Upon completion of the liquor cooking of the chips, valves 36 and 37 then opened whereupon the liquor is returned to the reservoir 33. After evacuation of the liquor from the vessel, valve 36 is closed and discharge valve 26 opened. Continued application of steam through valve 28 blows the cooked chips from the vesse] through discharge 18 into a receiver (not shown). Thereupon further processing of the cooked chips is determined by the end product desired.

It will be understood that the pulping and steaming process may vary to suit the different types of materials under treatment and the end productvdesired. Within the present concept of a rapid cycle digester is the advantageous treatment of wood chips of various species and combinations of species.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible of modification in its form, roportions, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise but one of several modes of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

Having thus described our invention, we claim:

1. Apparatus for pulping and steaming wood chips and like fibrous plant material, including a pressure vessel, means for introducing such material into said vessel, a source of steam for supply to said vessel, a reservoir of cooking liquor, feed and exhaust connections forming a closed fluid system between said reservoir and said vessel, a liquor pressure tank, means connecting said tank to said reservoir and into said closed fluid system, and means for placing the liquor in said tank under pressure.

2. Apparatus according to claim 1, characterized in that said last named means includes a pressure pump in the connection between said reservoir and said tank.

3. Apparatus according to claim 1, characterized by a connection from said source of steam to said tank and a shut-ofi valve in said connection.

References Cited in the file of this patent UNITED STATES PATENTS 1,138,907 Thickens May 11, 1915 1,459,913 Johnson June 26, 1923 1,922,262 Ross Aug. 15, 1933 1,979,341 Olsen Nov. 6, 1934 2,080,078 Mason May 11, 1937 2,215,353 Gill Sept. 17, 1940 2,263,903 Pomilio Nov. 25, 1941 2,516,847 Boehm Aug. 1, 1950 2,606,114 Lewis Aug. 5, 1952 2,640,774 Ross et al. June 2, 1953 

